Validation and usability of modified palmoplantar psoriasis area and severity index in patients with palmoplantar psoriasis: A prospective longitudinal cohort study

Background Palmoplantar psoriasis (PPP), a troublesome variant, does not have any validated scoring system to assess disease severity. Objective To validate modified Palmoplantar Psoriasis Area and Severity Index (m-PPPASI) in patients affected with PPP and to categorise it based on Dermatology Life Quality Index (DLQI). Methods In this prospective study, patients with PPP aged > 18 years visiting the psoriasis clinic at a tertiary care centre were included and requested to complete DLQI during each visit at baseline, 2nd week, 6th and 12th week. m-PPPASI was used by the raters to determine the disease severity. Results Overall, 73 patients were included. m-PPPASI demonstrated high internal consistency (α = 0.99), test-retest reliability of all three raters, that is, Adithya Nagendran (AN) (r = 0.99, p < 0.0001), Tarun Narang (TN) (r = 1.0, p < 0.0001) and Sunil Dogra (SD) (r = 1.0, p < 0.0001) and inter-rater agreement (intra-class correlation coefficient = 0.83). Face and content validity index for items I-CVI = 0.845 were robust, and the instrument was uniformly rated as easy to use (Likert scale 2) by all three raters. It was found to be responsive to change (r = 0.92, p < 0.0001). Minimal clinically important differences (MCID)-1 and MCID-2 calculated by receiver operating characteristic curve using DLQI as anchor were 2 and 35%, respectively. DLQI equivalent cutoff points for m-PPPASI were 0-5 for mild, 6-9 for moderate, 10-19 for severe, and 20-72 for very severe disease. Limitation Small sample size and single-center validation were the major limitations. m-PPPASI doesn't objectively measure all characteristics of PPP such as "fissuring" and "scaling" which could also be taken into consideration. Conclusion m-PPPASI is validated in PPP and can be readily utilized by physicians. However, further large-scale studies are needed.